tools/testing/selftests/powerpc/mm/large_vm_fork_separation.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 //
   3 // Copyright 2019, Michael Ellerman, IBM Corp.
   4 //
   5 // Test that allocating memory beyond the memory limit and then forking is
   6 // handled correctly, ie. the child is able to access the mappings beyond the
   7 // memory limit and the child's writes are not visible to the parent.
   8
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <sys/mman.h>
  12 #include <sys/types.h>
  13 #include <sys/wait.h>
  14 #include <unistd.h>
  15
  16 #include "utils.h"
  17
  18
  19 #ifndef MAP_FIXED_NOREPLACE
  20 #define MAP_FIXED_NOREPLACE     MAP_FIXED       // "Should be safe" above 512TB
  21 #endif
  22
  23
  24 static int test(void)
  25 {
  26         int p2c[2], c2p[2], rc, status, c, *p;
  27         unsigned long page_size;
  28         pid_t pid;
  29
  30         page_size = sysconf(_SC_PAGESIZE);
  31         SKIP_IF(page_size != 65536);
  32
  33         // Create a mapping at 512TB to allocate an extended_id
  34         p = mmap((void *)(512ul << 40), page_size, PROT_READ | PROT_WRITE,
  35                 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE, -1, 0);
  36         if (p == MAP_FAILED) {
  37                 perror("mmap");
  38                 printf("Error: couldn't mmap(), confirm kernel has 4TB support?\n");
  39                 return 1;
  40         }
  41
  42         printf("parent writing %p = 1\n", p);
  43         *p = 1;
  44
  45         FAIL_IF(pipe(p2c) == -1 || pipe(c2p) == -1);
  46
  47         pid = fork();
  48         if (pid == 0) {
  49                 FAIL_IF(read(p2c[0], &c, 1) != 1);
  50
  51                 pid = getpid();
  52                 printf("child writing  %p = %d\n", p, pid);
  53                 *p = pid;
  54
  55                 FAIL_IF(write(c2p[1], &c, 1) != 1);
  56                 FAIL_IF(read(p2c[0], &c, 1) != 1);
  57                 exit(0);
  58         }
  59
  60         c = 0;
  61         FAIL_IF(write(p2c[1], &c, 1) != 1);
  62         FAIL_IF(read(c2p[0], &c, 1) != 1);
  63
  64         // Prevent compiler optimisation
  65         barrier();
  66
  67         rc = 0;
  68         printf("parent reading %p = %d\n", p, *p);
  69         if (*p != 1) {
  70                 printf("Error: BUG! parent saw child's write! *p = %d\n", *p);
  71                 rc = 1;
  72         }
  73
  74         FAIL_IF(write(p2c[1], &c, 1) != 1);
  75         FAIL_IF(waitpid(pid, &status, 0) == -1);
  76         FAIL_IF(!WIFEXITED(status) || WEXITSTATUS(status));
  77
  78         if (rc == 0)
  79                 printf("success: test completed OK\n");
  80
  81         return rc;
  82 }
  83
  84 int main(void)
  85 {
  86         return test_harness(test, "large_vm_fork_separation");
  87 }